Enhanced removal of I− on hierarchically structured layered double hydroxides by in suit growth of Cu/Cu2O

Abstract To further improve the removal ability of layered double hydroxide (LDH) for iodide (I−) anions from wastewater, we prepared hierarchically porous Cu5Mg10Al5-LDH and used as a matrix for in suit growth of Cu/Cu2O on its surface, forming Cu/Cu2O-LDH, which was characterized and applied as an adsorbent. Results displayed high I− saturation uptake capability (137.8 mg/g) of Cu/Cu2O-LDH compared with Cu5Mg10Al5-LDH (26.4 mg/g) even thermal activated LDH (76.1 mg/g). Thermodynamic analysis showed that the reaction between I− anions and Cu/Cu2O-LDH is a spontaneous and exothermic. Uptake kinetics analysis exhibited that adsorption equilibrium can be reached after 265 min. Additionally, the adsorbent showed satisfactory selectivity in the presence of competitive anions (e.g., SO42−), and could achieve good adsorption performance in a wide pH range of 3–8. A cooperative adsorption mechanism was proposed on the basis of the following two aspects: (1) ion exchange between iodide and interlayer anions; (2) the adsorption performance of Cu, Cu(II) and Cu2O for I−. Meanwhile, the difference between the adsorption mechanism of Cu/Cu2O-LDH, Cu5Mg10Al5-LDH and Cu5Mg10Al5-CLDH adsorbents was also elaborated and verified.